The present invention relates to a method for manufacturing a molded body, particularly a prototype of a product or component, a tool prototype or spare part, in accordance with three-dimensional CAD data of a model of a molded body by depositing layers of a metallic material in powder form. Several layers of the powder are successively deposited one on top of the other, whereby each layer of powder is heated to a specified temperature by means of a focused laser beam applied to a given area corresponding to a selected cross-sectional area of the model of the molded body, before deposition of the next layer. The laser beam is guided over each layer of powder in accordance with the CAD cross-sectional data of the selected cross-sectional area of the model in such a way that each layer of powder is fixed to the layer below.
The increasing competitive pressure forces companies more and more not only to manufacture more economically with a constant high product quality but also to save time and costs in the area of product development. The life span of products is continuously shortened. In addition to product quality and product costs, the moment of market introduction is becoming increasingly important for the success of a product.
In many industry branches, it is necessary to manufacture prototypes prior to high-volume production, in order to install them already for testing purposes as functional components in test arrangements. Preferably, such prototypes correspond to the serial products not only in shape but should also be as close as possible to the serial product with regard to the material to be able to test such prototypes during the application.
For the above mentioned reasons, a technology for the above mentioned purposes has developed that is known as stereo lithography. Within the scope of stereo lithography, a prototype to be manufactured is divided into individual layers and the data of the individual layers concerning the prototype to be manufactured are supplied to a manufacturing device. Such a manufacturing device consists of a liquid bath with a UV hardening liquid that a UV beam sweeps over according to the contours and fields of the prototype to be manufactured in order to harden the liquid. Then, this initial layer is lowered to a defined layer thickness in order to harden a second coating on to it in accordance with the established data. Layer by layer this process continues until the entire model or prototype is created. Thin pipe walls, hollow cavities or intertwined components can be manufactured in a manner that corresponds to the serial product. Depending on the degree of partitioning of the layers, that is, the thickness of each layer that is hardened, even curvatures can be built in detail.
Aside from the stereo lithography where synthetic materials are hardened or polymerized using UV light, a method of building a prototype of sintered metallic material in powder form is known. Such a method is described in the International Patent Publication No. WO 92/10343. According to the method described in this document, in order to manufacture a component, a first layer of powder that can be sintered is deposited and the powder is sintered according to the layer areas of the part to be manufactured. Then, this method is repeated in a manner where each time a new layer is deposited on the previously sintered layer and where these layers correspond to the respective layers or cross-sectional areas of the component to be manufactured.
Known from "Heinz Hasenkampf et al, Laserstrahl-Sintern zur Herstellung von Blechformwerkzeugen "Laser Beam Sintering of Sheet Metal Forming Tools" in the magazine "BLECH ROHRE PROFILE" [SHEET METAL PIPES PROFILES], 43, 1996, pages 317 to 319, is a method for building up metal structures in layers by localized sintering, or melting together, of previously deposited metal powder layers using a focused laser beam. The metal structures are manufactured of materials in powder form without binding agent additives utilizing the melting phase, where several layers, each 0.1 to 0.2 mm in thickness, are deposited one on top of the other and are each radiated with a laser beam in a protective argon gas atmosphere.
A common disadvantage of the methods available on the market today, such as stereo lithography or sintering of metal powders, is that they cannot be used to manufacture metallic prototypes directly that can be employed in operational applications, for example, exhaust pipe elbows of a motor vehicle. The manufactured components are made of synthetic materials, metal, wax or paper that do not permit operational functional tests, particularly at high temperatures and high stress.
Concerning the sintering method, as it is also known from the document noted above, there are basically two methods currently pursued, one is direct sintering and the other is indirect sintering. With indirect sintering, the metallic powder material is sheathed with a polymer or with another sinterable sheathing material, such as a sintering agent that is necessary for such metals that by themselves are not sinterable. In the sintering process, only the polymer material or the sheathing material which is melted on or sintered and in this process binds the metal particles. However, the so-called blank manufactured in this manner still needs to undergo after-treatment in a separate process, for instance, surface smoothing or burning out of the binding agent made of polymer material. Alternatively, often such components must be densified and hardened by post-sintering and infiltration, which can result in shrinkage and deformation. With direct sintering, the powder mixture consists of a low melting point and a high melting point material. In processing, only the low melting point component is melted on and it functions as a binding agent-for the high melting point powder particles. This process has the disadvantage that the manufactured components have a density of less than about 80% and a low strength. Thus, a direct test or an employment of the component under operational or even extreme test conditions is not possible with this method variation as well.
A common disadvantage of the methods available on the market today, such as stereo lithography or sintering of metal powders, is that they cannot be used to manufacture metallic prototypes directly that can be employed in operational applications, for example, exhaust elbows of a motor vehicle. The manufactured components are made of synthetic materials, metal, wax or paper that do not permit operational functional tests, particularly at high temperatures and high stress.
Concerning the sintering method, as it is also known from the paper noted above, there are basically two methods currently pursued, one is direct sintering and the other is indirect sintering. With indirect sintering, the metallic material in powder form is sheathed with a polymer or with another sinterable sheathing material, such as a sintering agent that is necessary for such metals that by themselves are not sinterable. In the sintering process, only the polymer material or the sheathing material is melted on or sintered and in this process binds the metal particles. However, the so-called blank manufactured in this manner still needs to undergoes after-treatment in a separate process, for instance surface smoothing or burning out of the binding agent made of polymer material. Alternatively, often such components must be densified and hardened by post-sintering and infiltration, which can result in shrinkage and deformation. With direct sintering, the powder mixture consists of a low melting point and a high melting point material. In processing, only the low melting point component is melted on and it functions as binding agent for the high melting point powder particles. This process has the disadvantage that the manufactured components have a density of less than 80% and a low strength. Thus, a direct test or an employment of the component under operational or even extreme test conditions is not possible with this method variation as well.